Until someone compares the two I don't see how anyone could make that statement even if we are basing this on a pure issue of measurable things, such as dynamic range (which the D7100 may have as much as or more than the D600).
I may add that the removal of the AA filter from the D7100 will produce sharper images out of camera than the D600. Can D600 images be sharpened post processing to match, probably, if done correctly. This is but one example though of how blanket statements claiming camera supremacy are highly debatable. What if you are poor at sharpening or don't want to have to do it to every image?
Further, technology does not often tell the story: 'better images' are normally produced by 'better photographers' not 'better cameras'. I shoot FX now, but other than better noise suppression it doesn't do anything really 'better' than my D7000 did, just different at times.
p.s. Also if the D7100 doesn't spew debris and lubricant all over the sensor constantly it will definitely be the better camera